This invention relates to a disc brake caliper assembly, and more specifically, the invention relates to a disc brake caliper assembly that prevents piston knock-back.
Disc brake caliper assemblies are widely used in the automotive industry for applying a braking force to the wheels of a vehicle. The wheels are secured to a brake rotor, which has brake pads arranged on either side of its braking surfaces. A piston supported in the caliper housing forces the pads together and into engagement with the rotor when the vehicle operator depresses the brake pedal. Ideally, the brake pads do not engage the rotor when the brakes are not applied, which is a condition known as zero drag, so that frictional losses that reduce fuel economy are prevented. Typically, a retraction seal is used between the caliper housing and the piston to automatically retract the piston when the brakes are not applied.
Under severe operating conditions, the rotor may deflect due to vibrations or harsh road inputs. A deflected rotor may push back on the brake pads and force the piston into the caliper housing. As a result, an undesirable clearance between the rotor and brake pad may be created which increases the distance the operator must depress the brake pedal. Passive anti-knock-back devices have been employed, such as resilient rings, to prevent the piston from being forced into the caliper housing. However, as with many passive devices, the prior anti-knock-back device lacks fine control and responsiveness.
Electric parking brake actuators have been used to replace the mechanical devices typically employed to apply the parking brake. The electric actuators lock the piston in place once the brake pads have been forced together about the rotor. However, these actuators have been underutilized in that they only have been used for the limited purpose of applying the parking brake. Therefore, what is needed is an active anti-knock-back device that also may be incorporated into the electric parking brake actuator.
The present invention provides a disc brake caliper assembly having a housing with a bore and a piston disposed within the bore and movable between applied, retracted and knock-back positions. The piston is activatable by hydraulic pressure to move from the retracted position to the applied position; and a retracting seal is effective in the absence of the hydraulic pressure to move the piston from the applied position to the retracted position. A linkage adjacent the piston carries a stop; and an actuator is responsive to an end of brake activation signal to cause the linkage to engage the stop with the piston when the piston is retracted from its applied position to its retracted position so as to prevent the piston from moving from the retracted position to the knock-back position.
The actuator is preferably an electric motor that is ineffective to move the piston, through the linkage and stop, from the retracted position to the applied position. Thus, the motor may be activated to move the stop into engagement with the piston and then stall, with the stall being detected, for example by detecting a motor stall current increase; and the motor may then be deactivated in response. The end of brake activation signal is preferably provided by a brake position or pressure sensor.
The present invention prevents piston knock-back by moving the stop as required to engage the piston after each retraction of the piston into its retracted position, so that the piston cannot be knocked back by the brake disc beyond the retracted position. In so doing, the present invention automatically adjusts itself to brake pad wear as an additional benefit. Additionally, the apparatus of the invention is adaptable for use in an electronic parking brake with some additional software programming of the controller.